Generally, combustion turbines have three main assemblies, including a compressor assembly, a combustor assembly, and a turbine assembly. In operation, the compressor assembly compresses ambient air. The compressed air is channeled into the combustor assembly where it is mixed with a fuel. The fuel and compressed air mixture is ignited creating a heated working gas. The heated working gas is typically at a temperature of between 2500 to 2900° F. (1371 to 1593° C.), and is expanded through the turbine assembly. The turbine assembly generally includes a rotating assembly comprising a centrally located rotating shaft supporting rotor discs and a plurality of rows of rotating rotor blades attached thereto. A plurality of stationary vane assemblies including a plurality of stationary vanes are connected to a casing of the turbine and are located interposed between the rows of rotor blades. The expansion of the working gas through the rows of rotor blades and stationary vanes in the turbine assembly results in a transfer of energy from the working gas to the rotating assembly, causing rotation of the shaft. A known construction for a combustion turbine is described in U.S. Pat. No. 6,454,526, which patent is incorporated herein by reference.
It is known that higher inlet operating temperatures in the turbine assembly will provide higher thermal efficiency and specific power output. It is also known that the allowable stress to which the rotor blades of the turbine assembly can be subjected for a given blade life decreases with increasing temperatures of the working gas. Thus, a limiting factor in raising turbine efficiency and power output is the physical capability of the rotor blades in relation to the temperatures within the turbine.
Cooling the blades, or forming the blades from temperature resistant materials, or both, is often necessary to reach the desired inlet temperatures. Cooling the blades can be accomplished by using a cooling fluid, such as some of the air normally supplied to the turbine by the compressor in its regular mode of operation. It is known to provide radial passages for directing the cooling fluid through the blades where a portion of a blade may be abutted against a seal plate engaged in grooves in the rotor disc and in the blade. The seal plates may secure the blades to the rotor disc by preventing axial movement of the blades relative to blade mounting recesses in the disc. In addition, the seal plates may seal cooling fluid flow paths that extend to the upstream and/or downstream sides of the blades adjacent lower surfaces of blade platforms defining an inner flowpath for the working fluid.
U.S. Pat. No. 3,572,966 discloses a seal plate for rotor blades in which sideplates are described as fitting within grooves formed in a rotor disc and in rotor blades. The sideplates are located and retained in position by bolts and retaining pins and clips. In such an arrangement multiple parts must be manipulated during assembly, increasing the difficulty of the assembly operation, and maintenance difficulties may arise during disassembly due to breakage of the bolts.
U.S. Pat. No. 3,853,425 discloses a structure for sealing and locking rotor blades into a rotor, and for cooling the blades. The structure includes a plate at the downstream side of a cavity beneath each blade root and prevents cooling fluid in the cavity from leaking downstream out of the cavity. An inner edge of the plate fits in a groove formed on the rotor disc periphery, and an outer portion of the plate engages a groove in the blade root to prevent the plate from sliding circumferentially in the groove. An additional seal and locking plate is provided at the downstream side of the blade root and is locked in a groove in a blade platform to prevent axial movement of the blade. In addition, a special seal and locking plate is provided as the last plate to be inserted between the blade and the rotor disc which are inserted into a channel in the end of a rotor disc, and special indexing lock screws and lock washers are provided to hold the last plate in place.
Accordingly, there continues to be a need for a seal plate system that minimizes the number of parts requiring manipulation, and that enables the seal plate to be readily installed and removed from the blade supporting disc during maintenance operations.